[This is a rather controversial meteor radiant. Although weak evidence does
exist to suggest activity has emanated from the region of Upsilon Pegasi early
in August, too much hype over the years has produced a greatly distorted view of
the Upsilon Pegasids. After reading the following, please keep in mind that the
radiant produces weak activity that may never attain rates higher than one or
two meteors per hour, which makes it difficult to detect against the normal
sporadic background. In addition, the radiant may no longer produce activity as
there have been no confirmed observations since the mid-1980s.]
Harold R. Povenmire (Florida) discovered this shower on August 8, 1975,
while observing the Perseids. Three meteors were noted in a very short time
which originated from within the Great Square of Pegasus, but clouds prevented
more detailed observations. The next evening, Povenmire again detected the
shower and was able to determine the radiant as RA=350 deg, DECL=+19 deg.
Moonlight interfered with observations during 1976, but moonless nights
prevailed during early August 1977. An analysis by Sky & Telescope said
observers detected hourly rates as high as 8 to 13 on the evening of August 12
and 13, and Povenmire was quoted as saying that meteors were detected up to a
week before and after these dates. On the other hand, brief details published in
Meteor News seemed to cast doubt on the high rates and the results of 7
observers were summarized as indicating a maximum of only 1.71 per hour.
Moonlight was again no problem in 1978, but the confirming reports of
activity were also accompanied by reports with a negative tone. From Los Padres
National Forest in California, Mark Davis and Donald Gutierrez observed 20
meteors which originated within 20 deg of the Great Square of Pegasus during the
morning of August 12. On the other hand, Richard Nolthenius (Alpine, California)
made the comment, "Only six Pegasids were seen during 2 1/4 hours of observing
on the morning of the 13th. Due to the high rate of sporadic meteors this year,
my impression was that the number radiating from the Great Square was not much
more than would be expected by chance." Povenmire said that about 700 persons
around the world contributed observations, with some of the detailed
observations including color estimates of primarily yellow to white, and a
radiant diameter of about three degrees.
As these examples demonstrate, there were widely varying estimates of the
strength of Upsilon Pegasid activity. Subsequently, these conflicting
observations brought controversy and veteran meteor observer Norman W. McLeod
III (Miami, Florida) questioned the shower's very existence in the January 1979
issue of Meteor News.
McLeod listed at least 12 major and minor meteor showers which were active
during early August and in his evaluation of Upsilon Pegasid activity he said,
"Several of the named showers can account for the bulk of such meteors." He went
on to discuss his own observations, which generally revealed "only about 3
meteors/night from the Pegasid radiant" in early August. He added that his best
night was August 4/5 when 7 meteors were observed and that during the Perseid
maximum "only 1 Pegasid/night was seen."
The Author believes the Upsilon Pegasids were victim to a series of
unfortunate events which led many people to believe they were a potentially
major shower which peaked at the time of the Perseid maximum. This was far from
the truth. First of all, Sky & Telescope unfortunately did not discuss the
observations to their fullest, as the Upsilon Pegasid discussion occurred at the
end of a multi-page article dealing with the Perseids. The fact was that the
high rates quoted came from inexperienced observers who, as McLeod pointed out
above, simply confused meteors from several active showers with the Upsilon
Pegasid activity. What the magazine should have noted was that experienced
observers tended to reveal hourly rates of about 0-2 during the time of the
Perseid maximum and it is this fact that leads to the next problem. Despite
Povenmire's discovery of notable activity during August 8 and 9, 1975, observers
in 1977-1978 rarely observed any earlier than August 11. Since it is now
apparent that the Upsilon Pegasids rapidly weaken after their August 8 maximum,
no one would have expected these observers to see more than a few of these
meteors each night the Perseids were active.
Although a few meteor observers have continued to make this shower a
controversial subject, many others have helped to refine the current knowledge
of the Upsilon Pegasid stream. In the years following 1978, observers became
more aware of the earlier maximum for the Upsilon Pegasids and the picture soon
developed of a shower which produces maximum rates of 2 to 3 per hour.
The most significant visual study of this shower was made during July
30-August 16, 1983 by the Hungarian Meteor and Fireball Observation Network. In
the publication Meteor, Tepliczky István collated the observations and revealed
some interesting statistics concerning this shower's members. First of all, the
meteor colors were tabulated into the following percentages: 7% blue, 14%
blue-white, 28% white, 5% yellow-white, 32% yellow, 14% orange. Secondly, a good
record of the train activity of the shower was kept. Of 155 Upsilon Pegasids
observed, 20, or 13%, left persistent trains. Finally, ZHRs were computed for
each day, with a maximum of 5 being recorded on three occasions---August 1/2,
6/7 and 16. Maximum was plainly indicated as occurring during August 1-7, with
ZHRs remaining between 4 and 5, and the average ZHR being 4.6.
Aside from the estimates of hourly rates, one of the next most important
observations of any meteor shower is the determination of the average brightness
of its meteors. The average magnitude of the Upsilon Pegasids tends to be
fainter than for the other showers active during the first half of August and
this indicates a proportionately higher percentage of faint meteors than normal.
Norman McLeod, III (Florida) found the average magnitude to be 3.62 based on
meteors he observed during the period of 1977 to 1985. Robert Lunsford
(California) determined the average magnitude as 3.11 in 1979, 3.73 in 1980,
3.10 in 1981, and 3.59 in 1986. Pekka Parviainen (Finland) determined it as 2.90
in 1981. Data on the percentage of meteors leaving persistent trains has not
been frequently given, but, as noted earlier, it seems no higher than 13%.
As with all meteor showers, observations become more significant when
photographs are involved, and Povenmire's annual request for photographs of the
region have revealed several good specimens. Most notable has been the detection
of two meteors that appeared nearly stationary, thus giving an indication of the
general correctness of the original radiant estimate. In 1980, Steve Hunt
(Kansas City, Missouri) recorded a meteor "coming nearly head-on from the
radiant," while, in 1983, Leighton Venn (Bartlesville, Oklahoma) photographed a
nearly stationary Upsilon Pegasid which, when farthest from the radiant, was
only one degree away.
One of the best examples of a photographic Upsilon Pegasid was not
photographed by a regular watcher of this shower, but, instead, it was detected
by five cameras of the European Meteor Network on August 19, 1982. Network
director, Dr. Zdenek Ceplecha (Ondrejov Observatory, Czechoslovakia), made a
careful study of this fireball and proved that it was an Upsilon Pegasid. The
meteor was designated EN190882 and, when brightest, was about magnitude
13.8, or brighter than the full moon! Ceplecha's subsequent calculation of
a precise orbit gave the first indication of what the orbital plane of this
stream might look like (see "Orbit" section below).
Despite the evidence that has accumulated since this shower's discovery,
continued controversy as to the reality of this stream inspired the Author to
conduct an extensive search through publications of the last 100 years to
uncover past appearances. Overall, seven radiants are present which indicate a
duration extending at least from August 3 to August 11. The two earliest
observations were made by P. Denza and Alexander S. Herschel. The former
observer plotted several meteors from RA=350 deg, DECL=+24 deg on August 11,
1869, while Herschel's observations of 1860-1881 revealed a radiant at RA=345
deg, DECL=+15 deg on August 11. Cuno Hoffmeister's Meteorstrome (1948) revealed
three radiants. The first was located at RA=347 deg, DECL=+16 deg on August 3,
1913. The second radiant was at RA=352 deg, DECL=+18 deg on August 9, 1921. The
third radiant was at RA=352 deg, DECL=+18 deg on August 4, 1937. Finally,
American Meteor Society records reveal two radiants: one at RA=347.5 deg,
DECL=+22 deg on Augsut 4, 1924, and the other at RA=342 deg, DECL=+22 deg on
August 8.7, 1964.
Finally, in addition to searches for visual radiants, the Author has also
searched photographic records for double-station meteors. These meteors not only
offer reliable radiants, but, in many cases, they even offer orbital data. What
may be the very first double-station Upsilon Pegasid appears to have been
detected on August 3, 1902, during the Yale Photographic Meteor Survey, and
emanated from RA=346.4 deg, DECL=+17.8 deg. The inability to compute a velocity
prevented the calculation of an orbit and the radiant is not considered
absolutely certain. The next probable photographic Upsilon Pegasid appears among
the 2529 double-station meteor orbits computed by Richard McCrosky and Annette
Posen from data gathered during the Harvard Meteor Project. Designated 3607, the
meteor was detected on August 18.3, 1952, from RA=349 deg, DECL=+22 deg. Its
magnitude was 0.1, while the semimajor axis was computed as 13.47 AU. On August
13.8, 1958, a photographic survey conducted at Dushanbe (USSR) revealed a meteor
from RA=344.5 deg, DECL=+18.4 deg. The subsequent orbital calculation by Dr. P.
B. Babadzhanov revealed a slightly hyperbolic orbit with an eccentricity of
1.04.